Annalee Newitz

If you watch enough TV, you get the idea that the ideal mating combination is a skinny little woman and a burly man. But a new evolutionary study published in American Naturalist shows that's not what nature intended. In fact, the humble New Zealand weta (a relative of the cricket) demonstrates that evolution often pushes in the other direction: Only the smallest and most nimble weta males get to score with the sexy weta ladies who are twice their size. How could tiny males impress the weta females? Among these hopping insects, it's not uncommon for the males to travel up to 90 meters per night searching for a mate, which would be the equivalent of a human man walking 7 kilometers per night in search of a lady friend. Size does matter among the weta — it's just that being lightweight allows the male to show off his walking prowess much better than a large body would. Female wetas tend to walk much less, and when they do find a little male they like, they spend the whole next day mating with him nonstop. How do we know this, you ask? Apparently our group of researchers, who hail from Toronto, put microchips on male and female wetas and tracked them. Then, when these researchers found the mating wetas, they counted the empty sperm packets called "spermatophores" that were piled up around them. Then they could estimate whether weta who walked further got more chances with the old spermataphores. Know what I mean? Wink, wink, nudge, nudge? Said researcher Clint Kelly:

Our findings are a rare example of sexual selection favoring a suite of traits that promote greater mobility in one sex only. This is exciting because it suggests that sexual selection for smaller, more mobile males could be responsible for some of the impressive sexual difference in body size in this species.